EP 1 103 411 B1 discloses an adjusting device which is intended for a vehicle seat and has a first adjusting element and a second adjusting element, which is connected for movement purposes to the first adjusting element, in particular a device for adjusting an underframe of the vehicle seat longitudinally in relation to a seat part, wherein the adjusting device has a spindle and an associated spindle nut, which engages around the spindle, and wherein the spindle is fixed in a rotationally secured manner on the first adjusting element of the adjusting device and the spindle nut is mounted in a rotatable manner in the second adjusting element and, on its outer lateral surface, has a worm wheel, which is produced from plastics material and is in engagement with a worm, which can be connected to a rotary drive. At each of its two axial end regions, the spindle nut has a metal reinforcing barrel engaging around it, said reinforcing barrel enclosing the respective end region of the spindle nut in annular form and being connected thereto in a rotationally secured manner.